Monoscope cathode ray tube



' CHARACTER April 15, 1969 K, H. BRENNER, JR, ETAL 3,439,216

MONOSCOPE CATHODE RAY TUBE i Filed May 1, 19e? /0 Icann/TER I l D/5PMY`fZ3 l l SELc/croR l JN UT 55 I TJ k FROM scA/v GEA/RAME INVENTOR: /fuRr h'. BRM/Nm, Jk.

ATTORNEY United States Patent O U.S. Cl. 315-12 4 Claims ABSTRACT F THE DISCLOSURE An improved monoscope tube wherein a character stencil is positioned between an electron gun and .asecondary emitter, and la collector band is positioned between the electron gun and the character stencil. The character stencil surface and the secondary emitter `surface have high secondary electron emission rates. As the electrons from the electron beam strike the character stencil, secondary electrons are emitted from the stencil :and collected by the collector band thereby driving the character stencil positive. The electrons from the electron beam passing through the voids in the character stencil strike the secondary emitter causing secondary electrons to be emitted from the character stencil. The latter secondary electrons are collected `by the character stencil, driving the stencil negative.

Background of the invention This invention relates generally to cathode ray tubes and more particularly to improved monoscope cathode ray tubes.

The monoscope is a well-known cathode ray tube used, for example, to generate electrical signals representing alpha or numeric characters for display purposes or used to generate elcetrical signals representing broadcasting test patterns. In general a monoscope contains a target electrode which is sca-nned by an electron beam. The target has selected portions which produce different signal levels as it is scanned by the electron beam. In the prior art the target electrodes have generally been one of two types, the rst being a stencil target with the desired character pattern represented by voids in the stencil. The target is scanned by the electron beam which upon striking the stencil `surface genera-tes secondary electrons. A collector band having a positive potential with respect to the target is disposed adjacent the target and collects the secondary electrons. The signal taken from the target Varies in accordance with the number of secondary electrons emitted from the target surface. The electron bea-m when passing through the voids in the stencil pattern does not generate secondary electrons at the target and therefore establishes a zero reference level for the video signal.

The second commonly used monoscope construction utilizes a target upon which a character matrix of high carbon content has been deposited. A collector band, positive with respect to the target, attracts secondary electrons released from the target background as it is scanned by an electron beam. However, as the electron beam strikes the carbon characters, relatively few secondary electrons are lreleased so that the target is more negative when the beam scans the carbon matrix portion of the target. To provide adequate signal levels :and a satisfactory signal to noise ratio, extreme care and cleanliness is required in processing the target plate.

These prior art monoscope tubes require a relatively high electron beam current to achieve a video output signal voltage of suicient magnitude. The high beam current limits the resolution which may be attained by the tube. Furthermore, with higher Ibeam currents the 3,439,216 Patented Apr. 15, 1969 ICC useful operating life of the tube is adversely affected, since it is found that the secondary emission frate of the target material decreases more rapidly at higher beam currents.

Accordingly, it is lan object of this invention to provide an improved monoscope tube which overcomes the foregoing disadvantages and deficiencies of prior art devices.

Another object of this invention is to provide an improved monoscope tube which provides an adequate video output signal at a reduced level of electron beam current.

Still another object of this invention is to provide an improved monoscope tube having a longer useful operating life.

Summary of the invention According to one aspect of the invention, a monoscope is provided which utilizes both the electron beam striking the stencil target and the electron beam passing through the character voids in the stencil target to generate the video ouput signal. By thus using the entire electron beam, the desired level of Video output signal is attained with lower electron beam current.

Description of the drawings FIG. 1 is a block diagram of a system in which the monoscope tube of the present invention finds utility;

FIG. 2 is a plan view of a character stencil as utilized by the invention; and

FIG. 3 is a diagrammatic representation of the longitudinal cross-section of a monoscope tube according to the present invention.

Description of the preferred embodiments For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

Referring to FIG. 1, there is shown a computer 10 having its signal outputs 11 connected to the input of a monoscope tube 13. A scan generator 15 also applies input signals via lines 17 to the monoscope tube. The output of the monoscope tube is connected via a resistor 19 to a source of reference potential and is also applied to the input of an amplifier 21, the output of which is applied to a display device 23 and a printer 25.

In operation, the scan generator 15 provides electrical scan signals to the monoscope tube 13, the scan signals comprising a scanning raster which effectively encompasses the dimensions of a single character. The inputs 11 from the computer 10 to the monoscope 13 are electrical coordinate signals representing the location of the character on the character stencil within the monoscope tube to be scanned. For example, referring to the illustration of the character stencil shown in FIG. 2, in order to accomplish the scan of the letter F, one input from the computer is operative to select the rst column of the stencil and a second input from the computer selects the fourth row of the stencil as the row and column to be scanned. The input from the scan generator is a scanning raster one character high and one character wide; i.e. encompasses the dimensions of the box 29 surrounding the letter F. By superimposing the input signals from the scan generator 15 on the input signals from the computer 10, the selected character and only that character is scanned by the electron beam of the monoscope, thereby generating a video output signal representation of the character, which output is developed across the load resistor 19 and applied via the amplifier 21 to the display 23 and the printer 25 for further signal processing.

Referring next to FIG. 3, a monoscope tube 13 according to the present invention includes an electron gun 31 having a cathode element 33 connected to a source of energizing potential as represented by the terminal 35. The casing of the electron gun 31 is connected to a source of reference potential as represented by the terminal 37. A pair of vertical deflection plates 39 are disposed in front of the electron gun and are operative in response to the input signals to control the vertical scan of the electron beam from the electron gun, and in similar fashion a pair of horizontal deflection plates (not shown) control the horizontal scan of the electron beam. An anode ring 41 and a collector band 43 are positioned in the tube between the electron gun 31 and a character stencil 45 with the anode ring 41 and the collector band 43 being connected to suitable sources of reference potential as represented by terminals 47 and 49, respectively. The character stencil 45 is connected via the load resistor 19 to ground and also to a suitable signal amplifier such as the amplifier 21 of FIG. l. In front of the character stencil there is placed a secondary emitter 51 which is connected to a source of reference potential as represented by the terminal 53.

In a preferred operating mode, the sources of reference potential 37 and 47 are maintained near ground and the source of potential 35 applied to the cathode 33 is highly negative, i.e. 1200 to -1500 volts. The potential 49 applied to the collector band 43 maintains the collector band positive with respect to the character stencil 45, and the potential 53 applied to the secondary emitter 51 maintains the emitter 51 negative with respect to the character stencil. Both the character stencil and the secondary emitter are made from materials having secondary emission ratios which exceed unity. Now, as the electron beam scans the character stencil 45, those electrons striking the stencil generate secondary electrons which are emitted from the stencil and collected by the collector band 43, thereby driving the character stencil positive and developing a positive going potential across the load resistor 19. However, when the electron beam scans the voids in the character stencil, the beam impinges upon the secondary emitter 51 which also generates secondary electrons. Since the character stencil 45 is maintained positive with respect to the secondary emitter, the secondary electrons from the emitter 51 are collected by the character stencil thereby driving the stencil negative resulting in a negative going signal being developed across the output load 19. This effectively results in signal amplification from both the beam striking the character stencil surface and the surface of the secondary emitter so that a given output signal magnitude is attainable at a relatively low beam current.

With the monoscope tube 13 of the invention connected in the above described configuration, it is found that the life of the tube is extended primarily because the tube operates with lower beam current than prior art devices. However, it is found that the effective operating life of the tube may be extended even further by suitably changing the mode of operation. For example, if something should happen to adversely affect the secondary emission characteristics of the surface of the character stencil 45, the tube will still provide an adequate signal output if the beam current is increased and the collector band 43 is maintained negative with respect to the stencil, all other connections remaining unchanged. With this setup, the electrons of the electron beam which strike the character stencil contribute only minimally to the output signal, but the secondary electrons collected by the stencil resulting from the electron beam which passes through the voids in the stencil and strike the secondary emitter are sufficient to drive the character stencil negative to develop the necessary output signal magnitude. Conversely, it the emissive properties of the secondary 4 emitter 51 become adversely affected, the tube will still remain operative if the potential 53 is changed to maintain the character stencil negative with respect to the emitter 51. In the latter case, the full output signal is derived from the electrons in the electron beam striking the character stencil, as is the case with most prior art monoscope tubes.

It is therefore apparent that the monoscope tube of the present invention is a significant improvement over the tubes of the prior art. Since the output signal is derived not only from the electron beam striking the character stencil but also from the electron beam passing through the voids in the character stencil, a given output signal level is attained using a reduced level of electron beam current, thereby providing a tube having an extended operating life. Also, the tube remains operable even though the stencil or the secondary emitter may become defective during tube use, further extending the useful operating life of the tube.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

1. A character generating cathode ray tube comprising:

an elongated tube envelope;

an electron gun positioned near one end of said tube envelope and arranged to provide an electron beam along the axis of said envelope;

a secondary emitter formed of material having a secondary electron emission rate exceeding unity positioned near the other end of said tube envelope and arranged transversely in the path of said electron beam;

a character stencil formed of material having a secondary electron emission rate exceeding unity, said character stencil having a multiplicity of voids therein to thereby define a multiplicity of characters, said stencil positioned within said tube envelope between said electron gun and said secondary emitter and arranged transversely in the path of said electron beam;

a collector band positioned within said tube between said electron gun and said character stencil;

deflection means operative in response to input signals to scan said electron beam across selected characters on said character stencil; and p an output terminal connected to said character stencil.

2. The invention according to claim 1 additionally comprising:

first electrical potential means connected to said collector band and operative to maintain said collector band positive with respect to said character stencil; and

second electrical potential means connected to said secondary emitter operative to maintain said secondary emitter negative with respect to said character stencil.

3. The invention according to claim 1 additionally comprising:

first electrical potential means connected to said collector band operative to maintain said collector band negative with respect to said character stencil; and

second electrical potential means connected to said secondary emitter operative to maintain said secondary emitter negative with respect to said character stencil.

4. The invention according to claim 1 wherein said deliection means comprise first and second pairs of electrobetween said electron gun and said character stencil to static defiection plates positioned within said tube envelope 3,439,216 5 6 control, respectively, the horizontal and vertical scanning 3,336,498 8/ 1967 Castanera 315-18 of said electron beam.

RODNEY D. BENNETT, JR., Primary Examiner.

CHARLES L. WHITHAM, Assistant Examiner.

References Cited UNITED STATES PATENTS 5 3,278,794 10/1966 BoScia et al. 315-12 X US. C1. X.R. 3,336,497 8/1967 Osborne 315-18 315-21; 340-324 U.S. DEPARTMENT OF COMMERCE PATENT 0FFICE Washington,D.C. 20231 UNITED STATES PATENT OEEICE CERTIFICATE OF CORRECTION Patent No. 3,439,216 April l5, 1969 Kurt VH. Brenner, Jr., et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 75, cancel "static deflection plates positioned within said tube envelope" and insert the same in line 73, after "electro, same column 4.

Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, J r.

Commissioner of Patents Attesting Officer 

